Stronger regional differences due to large-scale atmospheric flow.

A new paper by Deser et al. (2012)(free access) is likely to have repercussions on discussions of local climate change adaptation. I think it caught some people by surprise, even if the results perhaps should not be so surprising. The range of possible local and regional climate outcomes may turn out to be larger than expected for regions such as North America and Europe.

Deser et al. imply that information about the future regional climate is more blurred than previously anticipated because of large-scale atmospheric flow responsible for variations in regional climates. They found that regional temperatures and precipitation for the next 50 years may be less predictable due to the chaotic nature of the large-scale atmospheric flow. This has implications for climate change downscaling and climate change adaptation, and suggests a need to anticipate a wider range of situations in climate risk analyses.

Although it has long been recognised that large-scale circulation regimes affect seasonal, inter-annual climate, and decadal variations, the expectations have been that anthropogenic climate changes will dominate on time scales longer than 50 years. For instance, an influential analysis by Hawking & Sutton (2009) (link to figures) has suggested that internal climate variability account for only about 20% of the variance over the British isles on a 50-year time scale.

I believe Deser et al.‘s results are important and a wake-up-call, because climate change projections used for the studies of climate change impacts have usually been based on a limited amount of regional climate model (RCM) and global climate model (GCM) simulations. Thus, they may not have sufficiently acknowledged the wide range due to internal variability.

Past research projects such as ENSEMBLES (25 runs with a combinations of RCMs/GCMs, thereof 13 independent GCMs simulations – link & final report), NARCCAP (5 independent simulations with GCMs – link), the UKCIP (11-member ensemble of RCMs), and PRUDENCE (included four different simulations with GCMs – assumed to reflect internal variability of climate (Beniston et al., 2007)) may not have — if Deser et al. are correct — accounted for the wide range of outcomes associated with different large-scale atmospheric flow.

The reason is that – separately – they imply a statistical sample (determined by the number of independent GCM simulations) of different large-scale atmospheric flows that may be too small to represent the actual range of possibilities.

Deser et al.‘s analysis was based on simulations carried out with one model (CCSM3), where they carried out nearly identical simulations 40 times which only differed by using slightly different starting points. Simulations carried out with one model, where the set-up is slightly different, is known in the climate science world as an single-model ensemble simulation.

The purpose of such ensemble runs is to explore the sensitivity of the predictions to different descriptions of the atmosphere at the start of the simulations. For instance the location and strengths of low- and high-pressure systems affect the flow of heat and moisture and the subsequent climatic evolution.

The importance of Deser et al.‘s findings can be seen in their figures (one reproduced below), where they highlighted the model simulations giving the smallest and greatest local response.

Figure 1 from Deser et al. (2012): The maps show the average response from the entire ensemble as well as the simulations which gave the warmest and coldest future. The middle panel shows the time evolution of the temperature at a selection of locations and averaged over areas (red curves mark the warmest simulations and blue the coldest). The right panel shows how many simulations in the ensemble that gave temperature trends of different values.

I think there were some surprising aspects in Deser et al.‘s results. Not that I didn’t expect natural multi-annual variations to be unimportant (on shorter time scales, they are very pronounced), but what strikes me is the strong contrast (on a 50-year time scale) between the global mean temperature (lower graph), which was not very sensitive to the regional atmospheric circulation, and the regional temperatures which were strongly influenced.

It has long been recognized that local and regional climate would warm at different rates than the global mean, but not with such large differences as presented by Deser et al. at the time scales of 50 years and for continental scales. Their results imply that while some regions could experience almost zero warming over 50 years, this will be compensated by substantially stronger in other regions (because they also find that the global mean temperatures to be largely insensitive to the different model initial conditions).

These results also imply a surprisingly long persistence of weather regimes in different parts of the world. Usually, one tends to associate these with inter-annual to decadal scales. However, Deser et al observe:

Such intrinsic climate fluctuations occur not only on interannual-to-decadal timescales but also over periods as long as 50 years… even trends over 50 years are subject to considerable uncertainty owing to natural variability.

These findings were in particular important for the winter season at mid-to-high latitudes. Hence, they could be entirely attributed to chaotic dynamics. On the other hand, the two simulations that they highlighted in their study represented extreme cases, and most of the simulations suggested that the future outcome may be somewhere in between.

My interpretation of Deser et al.‘s results is that the range of possible future temperatures gets broader at the same time as the most likely outcome follows a warming curve. This means that the most likely scenario is warming for the future while there still is a small possibility that the temperature for a particular location hardly changes (or even cools) over a 50-year period.

If each simulation is equally likely and the distribution of results given by the ensemble of runs gives an indication of likelihood, then the most likely outcome is described by the value that most of the ensemble members cluster around.

Another way to look at this is that the signal-to-noise ratio doesn’t increase much over time, which makes some of the take-home messages from Brown & Wilby (2012) important to heed. They argue that downscaling for the future involves too many unknowns, but can nevertheless provide tentative input to a more comprehensive risk assessment based on many factors, all of which may not necessarily be related to climate.

The Deser et al. paper also sends a message to people who study regional climate change based on a small selection of climate models (i.e. only from their own country). There is a need to include the maximum amount of reliable information about the local climate, and that would include the range of possibilities and the probabilities associated with these.

It is of course possible that the climate model used by Deser et al. exaggerates the variability in the large-scale atmospheric flow. However, their findings may also potentially explain the observation that led Oldenborgh et al. (2009) to conclude that Europe has warmed faster than projected by the climate models.

p.s. The ENSEMBLES project did involve a “grand ensemble” (climateprediction.net); however, this has so far not been used extensively for describing local and regional climate. The grand ensemble has been more appropriate for describing the global mean state and large-scale phenomena (link to experiments).

I’m surprised that models can show such great variability for both temperature and precipitation over the 50 year time scale. Under one of the “little change” scenarios for North America, does this disproportionate warming somewhere else in the world, or just that climate variability is somehow offsetting a substantial part of the warming predicted from simple calculations of total forcing? Looks like a really big play of the dice with future climate and weather.

I am surprised that models show such geat variability in their predictions for both temperature and precipitation over a region as large as the USA. Does this mean that global variability is also larger than previously expected, or that the warming predicted from simpler calculations of forcing is going to show up elsewhere on the globe under scenarios where the USA shows little change? Seem like a really big role of the dice for future climate and weather.

One question immediately occurs to me: Are the long-timescale regional variations only associated with climate change, or can they occur in a stable climate too? i.e. If the same ensemble were run with constant forcings, would you see places which could get either significantly cooler or warmer depending only on the starting point of the simulation?

A good metaphor for the climate system are probably the many gears of a clock. While the smaller gears create local variability, and the big gear position once altered to a certain threshold can change an entire regime to a different setup (climate state switch). This setup with “a climate on steroids”, hence more unbalanced, will accelerate all the gears in the clock.

Another conclusion is that CCSM3 is very sensitive to the skill of the user, and that the quality of the output is related to the quality of the input. Another conclusion is that a group working with CCSM3 can (unintentionally) push the output one way or another resulting in CCSM3 acting like a giant Ouija board the tells the group what the group collectively expects.

What I do not see in this are the atmospheric circulation changes that we have seen as the GIS has become the “cold pole” and cold continent/warm ocean & cold ocean/warn continent temperature differentials become larger relative to the tropical/Arctic temperature differential.

I expect atmospheric circulation patterns will become pinned to geographic features, and CCSM3 does not have the resolution to show how a localized cold pole would interact with the jet stream. Some of what looks like natural variability, may just be a lack of resolution in the model.

The lack of resolution in CCSM3 can mask the intensity and sustained duration of impacts and effects at specific locations.

For example CCSM3 does not see the Arctic sea ice loss of the last 5 years, and thus does not see the follow-on feedbacks from such loss. This is 2 strikes against CCSM3. It does not see the carbon feedbacks that are beginning to be detected. Three strikes!

CCSM3 is for teaching /academic insight. This tool is not suitable for use as a sole basis for engineering, risk management, or public policy.

[Response: I’m not sure why you have it in for CCSM3, or why you think any of these issues are relevant to the topic at hand. Your last argument is a bit of strawman. – gavin]

Dear Kevin
When looking at the figures presented in the paper, it seems that the climate begins to get a change only after 2005.
If extended linear trends proposed for 2005-2060 , all previous values ​​of 2005 to give lower than the average.
Or did not figure, or there is an error in these trends.
Even being tendencies to the future, they should in a short period for the past following data ever measured.
It seems to me that the work puts the year 2005 as the beginning of global warming. For before this year, the data are in line with the average.

If I understand this paper one of points it hopes to make is that on a regional scale, NATURAL climate variations may overwhelm the UNNATURAL variations that result from human activity.

Consider a few of the natural variations of the Arctic: the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), the North Pacific Decadal Oscillation, teleconnections with El Nino/Southern Oscillation (ENSO).

Regional climate modeling of the Arctic must be a nightmare. Is it any wonder that modeling one aspect of the Arctic climate system doesn’t match up perfectly with reality?

Doesn’t mean that people like Deser & Gavin shouldn’t keep on modeling.

BillD @1 — I’m an amateur at this. However I have looked at enough data, sometimes with the aid of simple (two+ box) climate models, to offer the opinion that global climate variability is fairly well characterized. It is at the regional scale that unpredictability sets in.

I do fully appreciate the fact that global warming will affect different regions of the world at different rates, and understand that a few areas could even expect some cooling while other areas get much warmer. However, I am surprised by the above maps. Alaska, in particular, seems to defy logic as it appears to be getting cooler while everywhere else in North America warms up. Since it’s almost certain that global warming will hit the northern polar regions particularly hard, a cooling Alaska is not what I’d expect, and I’m curious as to what the explanation for that is. However, I don’t have the scientific expertise to question these results, just curious as to why. It’s too bad these maps don’t cover the rest of the world – what will happen to Siberia, for example, would be interesting.

One thing I do feel confident predicting: Having visited Alaska and seen first hand the mostly conservative nature of the state’s politics, I’m sure that many of the residents will cite any local cooling as “proof” of the “global warming hoax,” even as sea levels rise and inundate their seaports and climate refugees flood into their state, there will be denial of the laws of physics to the bitter end.

Not that I didn’t expect natural multi-annual variations to be unimportant…

Apologies if I’m misunderstanding but shouldn’t this be “Not that I expected natural multi-annual variations to be unimportant…”? One too many negatives…

I note with interest that the worst case scenario for Massachusetts (where I happen to live) is 4 to 5 degrees C. I had previously read that that Boston is expected to attain a climate similar to Charlotte, North Carolina or Atlanta, Georgia (Northeast Climate Impacts Assessment 2007, see here). Dreser et al. lends credence to that projection. Palm trees (in the neighborhoods that aren’t submerged)?

The implication of Deser et al seems to be that regional projections do not add information – the global projection is as good a projection for a region as one can get with current models and data. The key issue is whether projections for individual sites are statistically significantly different from the global projections. Deser did not run those tests, but from the charts given it seems that the uncertainty of the local projected trends is so large that one cannot say they differ from the global projected trend. One probably is not justified in saying that a particular area will not experience warming, while another will experience unusually severe warming.

Scary stuff.
The temperature charts are bad enough, but the moisture charts are really scary. After last summer’s drought the driest prediction suggesting there is a possibility of the mid-west and west having a precipitation decrease of 20-30% is unimaginable. Unimaginable even after watching the Ken Burn’s documentary on the Dust Bowl.
Keep up the great work, and thanks.

Re: T Marvell: so where are we? I think a renewed study of regional paleoclimates would be useful. For example, studies of the climate of the Great Basin in the western U.S. show surprising changes in rainfall and evaporation that sometimes drove lake levels up or down counterintuitive to what changes in the broader global climate would predict.

I guess the question on my mind, is does Deser imply that variability is going to increase with time/warming, or does he say that even in an unmodified global climate it is larger than we thought? Those don’t have to be mutually exclusive either

[Response: Deser is a ‘she’, and this is a study focused on ensemble spread in the future, not the spread in the future ensemble spread if you follow me…. – gavin]

Thomas @19 — Good questions. I opine the answer to the first is we don’t know. As regards unmodified climate, paleoclimatological studies keep showing just how variable regional climates can be. It is larger than I had thought.

Re: Comment by John E. Pearson — 21 Nov 2012 @ 9:37 AM
12 Candide on Alaska. I’m not sure we’re looking at the same maps? My reading says the model averaged warming in alaska is somewhere between 4-6C/55 years. I don’t know how you see cooling.

Hi, JP. I’ve looked again, and it still looks that way to me. Comparing the two maps labeled “Warmest” and “Coolest,” Alaska looks like it will be considerably warmer in the “Coolest” map. But the rest of North America (especially the eastern half) looks like it will be getting a lot warmer.

Of course, these are computer models. No one can be totally sure how it will play out. But I’m not questioning the premise that we will overall have a much warmer world in the coming decades. This year’s dramatic meltdown of the north polar sea ice and Hurricane Sandy were just preludes to what will likely be major disasters. I feel sorry for the young people who will inherit this mess that my generation is leaving them (while so many of my age continue to deny this is even happening).

Re: Comment by John E. Pearson — 21 Nov 2012 @ 9:37 AM
12 Candide on Alaska. I’m not sure we’re looking at the same maps? My reading says the model averaged warming in alaska is somewhere between 4-6C/55 years. I don’t know how you see cooling.

Hi, JP. I’ve looked again, and it still looks that way to me. Comparing the two maps labeled “Warmest” and “Coolest,” Alaska looks like it will be considerably warmer in the “Coolest” map. But the rest of North America (especially the eastern half) looks like it will be getting a lot warmer.

Of course, these are computer models. No one can be totally sure how it will play out. But I’m not questioning the premise that we will overall have a much warmer world in the coming decades. This year’s dramatic meltdown of the north polar sea ice and Hurricane Sandy were just preludes to what will likely be major disasters. I feel sorry for the young people who will inherit this mess that my generation is leaving them (while so many of my age continue to deny this is even happening).

P.S. – I am having a terrible time with this ReCaptcha thing, with it often not telling me if my post succeeded or not. So this is the second attempt and if this comment appears twice, I apologize in advance.

Does this have anything to do with CC increasing arctic amplification, negative arctic oscillations, etc, thereby bringing more frequent killing freezes to our winter gardens here in the lower Rio Grande Valley, a subtropical area at latitude 26.3N?

wili @25 — Starting the GCM with different regional distributions of heat (just pushing it around, not changing the total) doesn’t affect (much) the global temperatures, just the eventual regional distribution.

Candide,
You are correct. Alaska has not witnessed the warming experienced by the rest of the globe during the past three decades. The locals know this, but it has apparently been lost on the clientele here.

[Response: Your continual making of baseless claims with no actual citation has not been lost on the clientele here at all. Regional Climate Change in Alaska. Since I don’t have time or energy to check every random claim you make, no unsupported statements of facts from you will be approved from now on. Either cite something that actually supports your claim, or don’t bother. – gavin]

Some local reporting from Alaska, with apologies for stealing content from Arthur Smith. There’s lots more at ClimateCentral with *real* news, not the manufactured kind promulgated by the anti-realist cabal. This moving observation was reposted at Neven’s and some other locations.

By Arthur C. Smith III (Kaktovik, Alaska, 99747) 20 Nov 2012
I’m glad to see in print, the report of what we have experienced up here and how significantly these details relate to a changing climate.

I live in Kaktovik, Alaska, which is on a small island in the Beaufort Sea, approximately 350 miles to the east of Barrow.

I believe for the first time in human history, the entire north coast of Alaska was ice free on November 1st; the Arctic Ocean was open and had reached a new record minimum for that date.

The world cannot underestimate the impact upon climate presented by such a large, newly opened body of water. Personally, I believe that the 2012 record Arctic sea ice minimum has crossed a threshold: the “tipping point” has been reached. The change in weather speaks to it, the change in animal behavior speaks to it, life in the arctic screams it… but will we listen?
Here in the Arctic, there is no choice but to listen, to see that daily life is changing in real time. I have lived here only nine years but in that short period of time, the change that I’ve witnessed is profound, to put it mildly.

Speaking of mildly, just to clarify the relative nature of the reader’s interpretation of the word “mild” being used to describe the start of the Alaskan Arctic winter. It is true that we’ve had a record warm September, warmer than normal temperatures in October and November, but the mitigation of temperature by open water has paled in the face of raging blizzards, one after another, week upon week, winds blowing in the 50s mph for days upon days, gusts in the 70s, record snowfall, aviation grounded, life at a standstill. Only here, can this scenario pass as quasi normal and equally pass unnoticed by the outside world. Anywhere in the lower 48, these conditions would merit national news coverage and likely some emergency relief.

But… the water is warmer, it is open. The air temperatures are warmer and the resultant increase in atmospheric energy has defined a fall, here in this part of the world, that no man living has ever seen; that no recorded history has ever documented. If not already on notice due the course of world climate events, be assured that the current exception of the Arctic experiencing “what no man has ever seen” will soon be shared by all man.

Alaska is strongly influenced by the PDO, which was in a positive temperature phase between 1976 to about 2005 and seems to be entering a negative phase since. Like everywhere else, temperature trends vary by location in the state. Barrow has been warming over the last few decades while trends in many other locations were flat.

Dave Person: You are posting in defense of “Dan H.” In my past Internet conversations with Dan H, he has posted under other pseudonyms, sometimes sharing the pseudonym with other authors; he has even occasionally supported his own arguments in these discussions by posting under still other pseudonyms. In fact, I have never seen him post under his real name. In your short message, you have demonstrated some of Dan H’s mannerisms, but for now I will give you the benefit of the doubt and assume that you are, indeed, a different “person.”

I post under my real name. There is only 1 person named Craig Nazor in the US (probably in the world).

In the link that Gavin provided (Berkeley Earth, or BE), the first chart is one of Alaskan annual mean temperatures. In the first link you provided, the second illustration is to a superficially similar chart (but unlike BE, which has a whole panel of scientists, this chart is apparently overseen by a Dr. Gerd Wendler, or GE). Upon close examination, the charts are actually quite different. The BE chart runs from 1830-2010, while the GE chart runs from 1949-2011. The BE chart features a 10 year running average, while the GE chart has a gray line which apparently indicates a 5 year running average. The BE chart provides a link to the description of how their raw data was obtained and provides the data; the GE chart does not. Lacking more documentation for the GE chart to make a better comparison, I was forced to do a little research on Dr. Gerd Wendler himself.

Gerd Wendler is a coauthor of this:

http://www.housemajority.org/coms/cli/uaf_gerhard_kramm.pdf
This appears to be a PDF to accompany a presentation to the conservative “House Majority” organization of the Alaskan Congress. At the end of the PDF, the summary includes: “The reasons for this [observed moderate climate] change can mainly be attributed to the change in the circulation pattern characterized by the change in the PDO index, rather than to the increase of the CO2 concentration. However, it is not known whether the change in the PDO index is affected by the rising CO2 concentration. “ It also includes: “Computer climate models are unable to even simulate major features of past climate such as the 100 thousand year cycles of ice ages that have dominated climate for the past 700 thousand years, and the very warm climates of the Miocene, Eocene, and Cretaceous. Neither do they do well at accounting for shorter period and less dramatic phenomena like El Niños, quasi-biennial oscillations, or intraseasonal oscillations – all of which are well documented in the data, as pointed out by Dr. Lindzen (MIT, 2001).” And this: “In contrast to the opinions of many Doomsday prophets like Tim Flannary [sic], a zoologist and the author of The Weather Makers, a ‘global warming frenzy’ and ‘a call to arms’ is, by far, not justified.”

This sounds pretty politically biased to me, and is not well supported by the science I have seen.

As Dan H knows, I am not a scientist, but I am very familiar with scholarly research. I am quite capable of evaluating information on the Internet. You are going to have to do better than this to convince me that “Alaska has not witnessed the warming experienced by the rest of the globe during the past three decades,” as Dan H claimed in #30.

By the way, your second link is to the home page of a web site. One of Dan H’s least endearing qualities is to link to papers that don’t actually support his contentions, but one has to read the entire paper to figure this out. I am not going to read and evaluate the entire web site. Is there anything SPECIFICALLY on this web site that you believe supports your claims?

Hi Craig,
I take no offence at your response to me but you are totally out of line with your comment. As a predator biologist for over 30 years, I’ve had to wear a thick skin longer than most climate scientists. My full name is Dr. Dave K. Person with the Alaska Dept. of Fish and Game and one of my interests involves predicting how climate changes will influence large terrestrial mammal ecological communities in SE Alaska. I posted the first link because it is sponsored by the University of Alaska Geophysical Institute, a highly reputable source. The data are what they are unless you believe the University of Alaska Fairbanks is committing fraud on their website. I did not post it to defend “Dan H”, whoever he is. The second link allows readers to explore some of the work in Alaska being done to project the consequences of climate change on the state climate and the arctic biome. I live in Alaska and observe some of these changes every year. Evidence of warming include glacial melting, thawing permafrost, lengthening growing seasons, range changes of plants and animals, etc. etc. etc. However, average temperature statewide does not provide a clear signal unless you filter out noise from processes like the PDO. The PDO cycle appears to be a dominant proximal player affecting our winter weather in SE Alaska, which affects how Sitka black-tailed deer survive, particularly when a great deal of their winter range has been clearcut logged. Warming is occurring but local processes obscure some of the warming signal for now, and consistent with the paper being discussed, those factors may result in unexpected variability. Indeed, after a period of almost 30 years of generally mild winters, we had a series of severely snowy winters which included the historic winter of 2006-2007. During that winter, snowfall reached 3 m at sea level in some places.

The caption for the temp. chart linked above from the Geophysical Institute says:

“the average change over the last 6 decades is 3.0°F…. The figure at right shows clearly that this trend is non-linear: a linear trend might have been expected from the fairly steady observed increase of CO2 during this time period.”

“… might have been expected …” is — wrong.

The source is unattributed for that too.
Who might have expected that?

DanH: “Alaska has not witnessed the warming experienced by the rest of the globe during the past three decades. The locals know this…”

Dave Person [an Alaskan “local”]: “Alaska is strongly influenced by the PDO, which was in a positive temperature phase between 1976 to about 2005 and seems to be entering a negative phase since. Like everywhere else, temperature trends vary by location in the state…”

Craig Nazor: “Dave Person: You are posting in defense of “Dan H.””

Really Craig, you need to lose the obsession on personalities. I read Daves link to a page topped by a graphic from The Alaska Climate Research Center as directly contradicting DanH’s hand waving, Alaska has obviously experienced warming in the past 3 decades, and Daves 2nd link very much fits with the lead post for this comment string, regional climate concerns. It’s not about conspiracy from the other “side” either.

It looks to me as though the temperature estimate from the Alaska Climate Research Center (ACRC) is a simple average of data from 20 locations. Most of them are in the southeast part of the state — in fact two of them are in or extremely near to the city of Fairbanks.

Alaska is huge, with those stations spanning over 1600 km in latitude alone. Therefore a simple average is inappropriate to characterize temperature for the state as a whole when the distribution of recording stations is so uneven — it gives far too much weight to the southeast region where data are concenrated and far too little to the northern and western part. The Alaska Climate Research Center should compute an area-weighted average by gridding, or by Krieging, in order to produce a graph which can properly be called “Alaska temperature.”

That is what is done in the Berkeley Earth temperature computation, which also includes data from a much larger number of locations. Therefore of the two, I regard the Berkeley earth result as a plausible representation of state-wide temperature while the ACRC result is not.

If Dave Persons is still reading, I suggest he pass this information along to those who produce the graphs.

Hi Hank,
Dr. Akasofu was the founding director of the Arctic Research Center at University of Alaska Fairbanks, not the Geophysical Institute, which was founded in the 1940’s. He directed the GI for a while in the 1990s but he is retired and was a well regarded auroral phycisist. He was not a climate scientist although he was skeptical of anthropogenic climate warming. I, however, am not. The GI houses many excellent scientists such as Chris Larson, Vlad Romanovsky. The Arctic Science Center also sponsors excellent work and has many well respected affiliated scientists such as Katey Walter Anthony. It is very unfair to impugn those research organizations because some members are skeptics regardless of how much you and I might disagree with their conclusions or actions.

With respect to “lake effect” snowfall, we generally have humid warm low pressure systems flowing in from the southeast. When they hit cold fronts (usually high pressure)from the north, we get snow. If the cold persists, we get more snow and if it stays for a long time, we get even more snow. We have had a string of these snowy winters in Southeast Alaska during the last 6 years with 2006-7 being by far the worst. It is rather disturbing watching deer starve to death while trapped along the beaches by deep snow.

I enjoy this website because it points me to information useful for my job. I am not here for entertainment. I have to use relevent climate data to evaluate the near- and long-term consequences of logging old-growth forest on ecological systems. There are those who argue that climate warming reduces the importance of preserving winter forest habitat for deer. They want to log it off. Over the next decade the negative-phase PDO likely increase the risk cooler snowy winters in SE Alaska despite long-term warming and winter range will be a critical factor sustaining deer.

This seems like a bit of a parlor trick. You’d expect the spread for the world to be smaller than the spread for the Unites States by a factor of 4 or so which is what happens in the simulation. Selecting the warmest and coolest runs does give long runs away from expectation, but that is a matter of selection, not new powers of weather over climate.

The range on drought realizations is certainly of interest and policy makers should certainly take note that food security needs to be carefully managed in the coming years.

The quarrel I have with the chart is the text that suggests temperature would be expected (by someone) to change linearly with CO2, and it doesn’t, and the conclusion is left to the misreader — that kind of thing is bait for that kind of reader who wants something to misunderstand.

Tamino’s criticism is more productive — a subset of sources used for the chart makes it easy to mislead the reader who wants to see epicycles.

> those who argue that climate warming reduces the importance
> of preserving winter forest habitat for deer.

Why depict anthropogenic greenhouse emissions as superimposed on ‘natural variability’? Setting aside astronomical forcings like solar cycles and cosmic ray fluxes, I can’t see any reason why we shouldn’t entertain the likelihood of interaction rather than simple addition. Indeed, the dichotomy seems more a matter of convenience than good physics. I concede, however, that the lack of real progress over the last 25 years in understanding the causality of Dansgaard-Oeschger oscillations – especially their faint echo in the Holocene – is afundamental obstacle to a more complete view.

I think you are confusing a statistical description with the physics. If not, what sort of interactions do you propose between natural events and greenhouse forcing? It is my understanding that most of the positive and negative forcings and feedbacks produce changes in temperature which, in turn, interact additively. For a very simple example- CO2, by itself, has little effect on the amount of water vapor in the atmosphere, but the temperature increase of the CO2 portion of the greenhouse effect does.

I am very sure that paleoclimate scientists are very motivated to understand Dansgaard-Oeschger events, but what importance do you think this has with regard to the current warming? Steve